Full keyboard access still not working on MacOs 12.3

Likewise it is dimmed out for me.

However, it can be enabled if you turn VoiceOver off.

So, presumably the two cannot be run at the same time. I don't know if this is a recent change or has always been the case.

I've asked Apple accessibility about that in February, here is the information I got from the emails exchanged:

"It is expected behavior for Full Keyboard Access to be dimmed while VoiceOver is enabled. Since both features accomplish a very similar tasks in allowing navigation with the keyboard, it is not feasible to have them both enabled at the same time. There aren’t any tasks that can be performed with Full Keyboard Access that cannot be performed with VoiceOver on its own."

"The Full Keyboard Access feature that appears in the Accessibility System Preferences was introduced in Monterey, and adds additional navigation functions to the keyboard, including grouped navigation. Since VoiceOver also navigates with groups, these features cannot be used in combination to avoid confusion.

However, the previous version of keyboard navigation is still available under System Preferences - Keyboard - Shortcuts - Use Keyboard Navigation to move focus between controls. In our testing, we were able to use the classic version of keyboard navigation along with VoiceOver in order to navigate app controls with Tab and Shift Tab."

I hope it helps :)